90991981 has 4 divisors (see below), whose sum is σ = 91030464. Its totient is φ = 90953500.

The previous prime is 90991961. The next prime is 90992017. The reversal of 90991981 is 18919909.

It is a semiprime because it is the product of two primes, and also a Blum integer, because the two primes are equal to 3 mod 4, and also an emirpimes, since its reverse is a distinct semiprime: 18919909 = 953 ⋅19853.

It is a cyclic number.

It is not a de Polignac number, because 90991981 - 2⁵ = 90991949 is a prime.

It is a super-2 number, since 2×90991981² = 16559081212608722, which contains 22 as substring.

It is a Duffinian number.

It is a congruent number.

It is not an unprimeable number, because it can be changed into a prime (90991961) by changing a digit.

It is a polite number, since it can be written in 3 ways as a sum of consecutive naturals, for example, 15445 + ... + 20506.

It is an arithmetic number, because the mean of its divisors is an integer number (22757616).

Almost surely, 2^90991981 is an apocalyptic number.

It is an amenable number.

90991981 is a deficient number, since it is larger than the sum of its proper divisors (38483).

90991981 is a wasteful number, since it uses less digits than its factorization.

90991981 is an evil number, because the sum of its binary digits is even.

The sum of its prime factors is 38482.

The product of its (nonzero) digits is 52488, while the sum is 46.

The square root of 90991981 is about 9538.9716951042. The cubic root of 90991981 is about 449.7809320543.

The spelling of 90991981 in words is "ninety million, nine hundred ninety-one thousand, nine hundred eighty-one".